1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the same, and more particularly, to a capacitor of a semiconductor device including a dielectric film of high dielectric constant (a high dielectric film) and a method for manufacturing the same.
2. Description of the Related Art
As an integration density of a semiconductor device such as a dynamic random access memory (DRAM) and a ferro-electric RAM (FRAM) increases, a high dielectric constant material such as PbZrTiO.sub.3 (PZT) or BaSrTiO.sub.3 (BST) is required for the dielectric film of a capacitor. Metals of the platinum group and the oxides thereof are mainly used for the conductive film forming a lower electrode or an upper electrode in a capacitor using the high dielectric film. Here, a dry etching for patterning the platinum group metals and the oxide thereof used for the conductive film of the capacitor is difficult. Also, since the platinum group and the oxide thereof reacts with a polysilicon film used as a contact plug, a diffusion barrier layer for preventing the reaction is required between the conductive film and the polysilicon film.
FIG. 1 is a sectional view for describing the capacitor of the semiconductor device according to a conventional technology.
To be specific, an interlayer dielectric film 3 having a contact hole is formed on a semiconductor substrate 1. A contact plug 5 comprised of the polysilicon film is buried in the contact hole. A diffusion barrier layer 7 connected to the contact plug 5 and comprised of Ta is formed. A first conductive film 9 used as the lower electrode of the capacitor and comprised of Pt is formed on the diffusion barrier layer 7. A high dielectric film 11 is formed on the overall surface of the semiconductor substrate 1 on which the first conductive material 9 is formed. A second conductive material 13 used as an upper electrode is formed on the overall surface of the semiconductor substrate 1 on which the high dielectric film 11 is formed.
In a conventional capacitor shown in FIG. 1, the diffusion barrier layer 7 is formed in order to prevent the reaction between the platinum film of the first conductive film 9 and the contact plug 5. In the conventional capacitor shown in FIG. 1, since the side surfaces of the platinum film of the first conductive film 9 and the diffusion barrier layer 7 are exposed during the deposition of the dielectric film 11 and in a subsequent heat treatment process, the diffusion barrier layer 7 is oxidized and thus becoming Ta.sub.2 O.sub.5 which is a non-conductor. Accordingly, the contact resistance of the first conductive film 9 increases and the first conductive film 9 cannot be used. Also, in the conventional capacitor shown in FIG. 1, leakage current increases since the diffusion barrier layer 7 reacts with the high dielectric film 11.
A method of recessing the contact plug is proposed in order to solve the above problem, which is described with reference to FIGS. 2 and 3.
FIGS. 2 and 3 are sectional views showing the capacitors of the semiconductor device according to another conventional technology.
Referring to FIGS. 2 and 3, an interlayer dielectric film 23 having a contact hole is formed on a semiconductor substrate 21. A silicon plug 25 and a diffusion barrier layer 27 comprised of Ta film are sequentially buried in the contact hole. A first conductive film 29 used as the lower electrode of the capacitor and comprised of Pt film is formed on the diffusion barrier layer 27.
In the conventional capacitor shown in FIG. 2, the diffusion barrier layer 27 is formed in a position different from that of the diffusion barrier layer 7 of FIG. 1. Namely, since the diffusion barrier layer 27 is buried in the contact hole, it is possible to prevent the side surface of the diffusion barrier layer 27 from being exposed.
However, in the conventional capacitor shown in FIG. 2, the diffusion path of an oxygen atom is short, and thus the diffusion barrier layer 27 may be oxidized during a subsequent process of forming the high dielectric film.
Furthermore, as shown in FIG. 3, when a misalignment occurs during patterning for forming the first conductive film 29, the diffusion barrier layer 27 is exposed and oxidized during the subsequent process of depositing the high dielectric film and becomes a nonconductor. When the diffusion barrier layer 27 becomes nonconductive, the contact resistance of the conductive film 29 is increased and the production yield of the semiconductor device is deteriorated.